Vitamin A deficiency associated with urinary retinol binding protein wasting in Dent's disease

Three patients with Dent's disease presented with complaints of impaired night vision or xerophthalmia and were found to have severely decreased serum retinol concentrations. Retinol, bound to its carrier retinol-binding protein (RBP), is filtered at the glomerulus and reabsorbed at the proximal tubule. We hypothesized that urinary loss of retinol-RBP complex is responsible for decreased serum retinol.

The study aim was to investigate vitamin A status and RBP in serum and urine of patients with genetically confirmed Dent's disease.

Eight patients were studied, three boys had clinical vitamin A deficiency, three had asymptomatic deficiency, and two young men with Dent's disease and impaired renal function had normal retinol values. Serum RBP concentrations were low in patients with vitamin A deficiency and were correlated with vitamin A levels. Urinary RBP concentrations were increased in all patients (2,000-fold), regardless of vitamin A status. This was in contrast to patients with glomerular proteinuria who had only mildly increased urinary RBP with normal serum RBP and vitamin A, and patients with cystinosis with impaired renal function who had massive urinary RBP losses but without a decrease in serum RBP or vitamin A levels. Treatment with vitamin A supplements in patients with retinol deficiency resulted in rapid resolution of ocular symptoms and an increase in serum retinol concentrations.

Vitamin A deficiency is common in patients with Dent's disease and preserved renal function. We therefore recommend screening these patients for retinol deficiency and treating them before visual symptoms develop.